linux-kernel - [PATCH] arm64/sme: Drop inaccurate documentation of streaming mode switches

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Message-Id: <20250723-arm64-sme-mode-switch-doc-v1-1-702bb484b4f4@kernel.org>
Date: Wed, 23 Jul 2025 13:27:45 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>
Cc: Mark Rutland <mark.rutland@....com>, 
 linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: [PATCH] arm64/sme: Drop inaccurate documentation of streaming mode
 switches

The SME ABI documentation contains an inaccurate description of the
architectural streaming mode entry/exit behaviour, just remove it since
this is better documented by the architecture or with the rest of the
documentation for the specific software interfaces concerned.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
The rest of the documentation needs more thorough review, but it seems
wise to remove the incorrect statement to avoid confusion.
---
 Documentation/arch/arm64/sme.rst | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/Documentation/arch/arm64/sme.rst b/Documentation/arch/arm64/sme.rst
index 4cb38330e704..583f2ee9cb97 100644
--- a/Documentation/arch/arm64/sme.rst
+++ b/Documentation/arch/arm64/sme.rst
@@ -81,17 +81,7 @@ The ZA matrix is square with each side having as many bytes as a streaming
 mode SVE vector.
 
 
-3.  Sharing of streaming and non-streaming mode SVE state
----------------------------------------------------------
-
-It is implementation defined which if any parts of the SVE state are shared
-between streaming and non-streaming modes.  When switching between modes
-via software interfaces such as ptrace if no register content is provided as
-part of switching no state will be assumed to be shared and everything will
-be zeroed.
-
-
-4.  System call behaviour
+3.  System call behaviour
 -------------------------
 
 * On syscall PSTATE.ZA is preserved, if PSTATE.ZA==1 then the contents of the
@@ -112,7 +102,7 @@ be zeroed.
   exceptions for execve() described in section 6.
 
 
-5.  Signal handling
+4.  Signal handling
 -------------------
 
 * Signal handlers are invoked with PSTATE.SM=0, PSTATE.ZA=0, and TPIDR2_EL0=0.

---
base-commit: 86731a2a651e58953fc949573895f2fa6d456841
change-id: 20250722-arm64-sme-mode-switch-doc-8e132434b4ed

Best regards,
--  
Mark Brown <broonie@...nel.org>